1. Field of the Invention
The present invention relates to a method for transmitting orthogonal frequency division multiplexing (OFDM) signals, and a transmitter and receiver thereof.
2. Description of the Related Art
In a multipath channel, in an environment where signals arrive with different propagation delay time, wave distortion caused by intersymbol interference can be a major factor of deteriorating communication quality. An orthogonal frequency division multiplexing (OFDM) scheme is known as a scheme to reduce wave distortion which occurs when receiving signals with different propagation delay time.
In the OFDM scheme, in order to compensate a residual phase offset attributable to clock offset or frequency offset, a method is known in which a known signal referred to as a pilot signal is allocated to a particular subcarrier and transmitted from a transmitting side as described in “High-speed physical layer in 5 GHz band part 11: Wireless LAN medium access control (MAC) and physical layer (PHY) specifications”, IEEE 802.11a, “17.3.3 and 17.3.5.8 (referred to as document 1, hereinafter). At a receiving side, demodulation accuracy of a data signal is improved by estimating and compensating the residual phase offset using the pilot signal.
Generally, as an OFDM signal is transmitted as a complex signal, an orthogonal modulator is used at the transmitting side. In the orthogonal modulator, in some cases, an amplitude error or phrase error may occur between an inphase component and an orthogonal component, which is referred to as an IQ imbalance distortion. In the case of using the pilot signal described in document 1, in an environment in which an IQ imbalance distortion occurs, there is a problem that the residual phase offset of the data signal cannot be compensated sufficiently due to an error in the estimation of the residual phase offset component.